struct Order{
    id: u32,
    name: String,
}
impl Order{
    fn new(id: u32, name: String) -> Order {
            Order {
               id,
               name
            }
    }
    fn show(&self){
        println!("id: {}, name:{}", self.id, self.name);
    }
    fn set_id(&mut self, id: u32){
        self.id = id;
    }
}
#[test]
pub fn order_test(){
    let mut order: Order = Order::new(12_u32, String::from("李四"));
    order.show();
    order.id = 2334;
    order.show();
    order.set_id(45_u32);
    order.show();
}


struct Grade{
    id: i32,
    name: String,
    stu: Option<Box<Student>>, //使用Box指针
}

struct Student {
    id: i32,
    name: String,
    grade: Grade,
}